Process of producing stencils



Feb. 1, 1944. Y E. o. NORRls PROCESS OF PRODUCING STENCILS 2Sheets-Sheet l Filed June 5, 1941 INVENTOR libwww 0. MHP/.

ATTORNEY Feb. 1, 1944. E o, NORRIS 2,340,485

PROCESS 0F PRODUCING STENGILS Filed June 5. 1941 2 Sheets-Sheet 2 50lNvEN-roR fon/A RD /VoHH/s ATTORNEY UNITED STATT-:s PATENT o1-FicaPROCESS F PRUDUCING STENGILS Edward 0. Norris, Westport, Conn., assignorto Edward 0. Norris, Ine., New

poration of New York Application June 5, 1941, Serial No. 396,681

11 claims.Y (ci. 2 04-.11)

This application is a continuation-impart of myco-pending applicationSer. No. 376,769, led January 31, 1941, now Patent No. 2,282,203, May 5,1942.

The invention relates to as are used for making ink and paintimpressions of designs, depositing adhesive in the form of a a design,and in general making impressions of a large variety of materials. Moreparticularly, it relates to processes of producing stencils of thegeneral character just described, so constructed that fine lines of thedesign to be impressed or printed are clearly defined and unbroken, andthe edges of larger areas are clearly demarked and free from the raggedor saw-tooth appearance which often characterizes work done with theordinary screen stencil.

The objects will be presently more clearly brought out as the stencilitself and the mode4 of constructing it are explained in connection withthe drawings.

AReferring to the drawings, Y

Fig. 1 is an isometric view showing a portion of stencil base whichconsists preferably of electroformed foraminous sheet. On` the sheet isindicated an area in thel form of an annulus which may be taken forpurposes of illustration as the design that is to be printed orimpressed;

Fig. 2 is an isometric view showing the foraminous sheet oi!i Fig. 1covered with two successive layers of material in association withaprinting plate; l

Fig. 3 is an isometric view showing the design blocked out;

Figs. 4 and 5 show successive steps in theprocess; Fig. 6 shows acompletedstencil;

Figs. 7-12 show a modication of the process. It is to be realized thatthe drawings are on a vastly larger scale than would be employed inpractice. vUsually the yhase screen would have in the order of from 25to 100 meshes to the linear inch, and as much as possible .of the areawould be open, the limit of open area obviously being ilxed by thestrength of the material, the nature of the use to which the stencil isto be put, etc. In most cases the design would be of a more elaboratenature than what I show in the drawings. However, the principle involvedin my invention is the same regardless of the elaborateness of thedesign, and so I have selected a very simple one by which to explain theprocess-an the linal product. l

screen stencils such i 'design for flock-printing, applying dyes to formknown as lands.

York, N. Y., a cor- Fig. 1 shows a portion of an electroformed screenconsisting of the wires I9 intersected normally by the wires il.Preferably, as stated above, the open areas I2 are as large as possibleconsistent with suitable structural strength. Such a screen and a methodof producing it by electroforming on a matrix are illustrated anddescribed in my United States Patent No. 2,166,366 issued July 18, 1939,and therefore it is not necessary at present to go into details as tohow the screen itself is produced.

In using the term wires to describe the component parts of the screenstructure, I am aware that the wordA is used in a sense somewhat be yondthe usual. However, it is afact that a true wire structure, such aswoven wire screen, would serve my purposes, although, as I have found,not as satisfactorily as does the electroformed screen. In screen of theelectroformed type, what I have termed wires are frequently In general,such screen structures may be termed mesh fabric, which includes, in theordinary accepted meaning of the term, not only woven fabric but alsothat which is punched. etched or electroformed as well.

To make the process clear, I have shown on Fig. 1 in dotted lines anannular'area which will correspond with the open area of the completedstencil, the remaining areas of the stencil of course being blockedout,as will be presently described, by imperforate sheet superimposedthereon. 1

In order to make clear the description, it should be explained that itinvolves selective etchingi. e., the employment of etching agents thatcorrosively react on one material to the exclusion of another, and toavoid complicated language it will be assumed that the material of thebase screen is of nickel. 0n the nickel screen which will eventuallyserve as a backing for the layers of imperforate material to be laidthereon, is deposited a layery I3 of copper, the copper completelycovering the base screen itself to a substantial thickness. copper isap#- plied preferably by electroplating, the bottom (with reference tothe orientation of the screen as shown in the drawing) being suitablymaskedV by covering with waxed paper or according to other methodswell-known in the electroplatlng and electroforming arts. As an incidentto the electroplating step (unless the holes are iirst filled `withelectrically non-conductive material) the copper not only overlies thebase screen but it also extends into the holes. As will be apparenthowever, as the description goes on, it is merely necessary that thecopper overlie the screen.

The next step consists in applying to the copper layer thelight-sensitive layer 20 of photoengravers glue, cr light-sensitizedshellac. The Well-known coatings known as Coldtop and Gluetop also servethe purpose very well. The

particular type of coatingis not, however, im-.

portant, provided that when developed it is passive to electrolyticdepositiongand is not deleteriously aiected by the electrolyte which'will be employed in a subseq'uent step, as will be later explained.

The next step (see Figs. 2 and 3) is to photoprint the design on thecoating of light-sensitive material, which is accomplished by means ofthe coat is then developed by washing in water if the Gluetop is used,consequently exposing the copper as shown. in Fig. 3, where previouslycovered by the opaque area. If shellac be used, the developing could becarried out with an alcoholic preparation sold under the tradename of"Chemco Glascote Developer. The isteps of blocking out the-design on thecopper are wellknown and need no detailed or further description. Itmight be added, however, that the developed coat 24 that blocks out thedesign should preferably be further hardened by baking.

A step that may be carried out at this stage, although it could as wellbe carried out at any time after the copper layer I3 has been deposited,consists in applying to the bottom of the screen a very thin layer 30 ofnickel which covers `the screen itself as well as the copper and formswebs, bridging the apertures in the screen. It should be noted that theterm .very thin is used relatively in comparison with the mesh number ofthe screen, its thickness, and the thickness of the 'copper layer-forexample, in the caseof a 1D0-mesh screen (100 screen units to the linearinch), and with the screen itself .005 thick and the copper the same,the thickness of the layer could properly be in the order of .00005".The same proportions would serve as the screen units per linear inchwere increased or decreased from the assumed number. The important thingis that its strength shall be suflicient to withstand the handling towhich the structure will besubjected in the course of applying a heavylayer of nickel presently to be referred to; on the other hand, itshould preferably be no thicker than is suflicient to serve this purposesince, a's will further appear, it should be possible to etch it quicklythrough without removing any substantial amount of material from therest of the structure. The thin layer 30 reached. These results can beaccomplished with a suflicient degree of accuracyV by properly adjustingthe thickness of the copper layer with respect to the width of the bandof glue and with respect to the width and height of the screen wires. Inother words. if the band of glue be excessively narrow, the etchant willreach the screen wires before -the copper has been undercut o'rsuiciently undercut beneath the glue band, and, as will become obvious,after the full process -has been explained, it would then not bepossible to etch the ink-feeding passages from one face of the stencilto theother. A suitable etchantfor the combination of materials thathave been specifiedA by way of example, is chromic acid inasmuch as,although it readily etches the copper, it does not affect the band ofhardened glue nor the material of the screen nor the layer 30 of nickel.There is then applied by electroplating a heavy deposit 3l of nickel.'I'his deposit covers the wires of the screen, the areas of the layer'30that are exposedbetween the meshes of the screen with or without aresidual layer of copper dependent upon the stage at which the copperetching step has been arrested, and also what is left of the copperlayer I3 beneath the band of glue; and its upward growth is limited. bythe overhang o'f the latter. The thickness of this heavy depositV issuch as to give it the necessary strength to withstand the printingpressures to which the stencil will be subjected in actual use withoutcollapsing and blocking the ink passages which will subsequently beopened up. This point lwill become clear as the description proceeds.

The heavy deposit of nickel having been applied, the band 24 of thedeveloped glue is removed by thek application, for example, of caustichaving'been-applied, the structure Yof Fig. 3 isv potash, and then whatis left o`f the copper layer I3 or most of it is etched Vo ut by chromicacid which has no effect or substantial effect on the nickel deposit 3|.This operation opens up passages through to the thin layer 3U of nickel.After removing the thin nickel layer 30, which may be doneby brushing,the result is shown in Fig. 6, where, as it will be observed, the fineline of the design is not blocked against the passage of ink by any ofthe wires of the screen. The layer 30 may also -be removed by anodictreatmentin a dilute sulphuric acid bath, which operation is promptlyarrested when passages have been completely opened up from the designareas around the wires of the screen lto its rear face. The object ofmaking the nickel layer 30 as thin as possible is now obvious. Its onlypurpose is to serve as a base in the apertures of the screen on whicht'o deposit th'e heavy nickel layer 3l. Therefore, it need be no thickernor stronger than is necessary to serve this purpose and to withstandthe handling that is necessary in applying the heavy nickel layer 3|.The thinner it is, the more easily may it be brushed orf to open up thepassages referred to; also, the thinner it is in comparison with thethickness of the heavy nickel layer 3I, the sooner the anodic treatmentmay be arrested and the less will be the amount of material removed fromthe heavy layer.

In applying the several layers of metal, electropl'ating actssatisfactorily. Where etching is referred to, electrolytic deplating isincluded wherever the process is applicable.

lThe advantages of the stencil can now be brought out more clearly thanbefore. By referring back to Fig. 1, it will be seen that, when thedesign includes fine lines such as the annular ordinary process ofsimply blocking out the stencil tovform the design leaves these finelines in many cases overlying and blocked by portions of the lands. Thismay be illustrated by reference to Fig. l, where, for example, a portionof the design traverses for a short distance the landA Ita as indicated.It also crosses various other lands and is blocked out by the land Il,Consequently, when a stencil of the simple forni just referred to isused for printing fine lineiigures. especially where the lines are aboutthe width ofr a screen unit or less, the-lines, when printed, appearbroken for the reason that the ink is not delivered atthose portionswhere the design is blocked out by the screen lands. By the term screenunit is meant the linear dimension of a wire and an adjacent aperturecombined.A My

stencil, however, is distinguished from the stand,

ard construction which I have described in that in the former' the fineline discharge orifice for the inkis ofpen at all points to the sourceof supply on the opposite or rear side of the stencil, and thus the inkor the like comes through freely, passing around the Wires of thescreen.

and thence through the discharge orifice in uniform volume and in anunbroken stream. As

an extension of the foregoing, the stencil also j has definiteadvantages even where an area covering many apertures of screen isopen,in that the edges of the printed design do not present a ragged orsaw-tooth appearance as they would and do where access 0f ink to them ispartially.

obstructed by the screen lands.

In explaining the invention I have up to this point preferred. for the-sake of clarity, to name a specific combination of materials indescribingl how it may be carried out. However, it will be seen that theunderlying principles do not necessarily involve the use of the specificmaterials that I have named; for example, if the base screen and thelayer were of copper instead of nickel, the 1ayer i3 could be of zincinstead ofcopper. In such case. obviously thechoice of etching agentswould need to be adapted to bring about the selective actions that arenecessary in the case just supposed; for' instance, the etchant for thezinc could be dilute sulphuric acid since dilute sulphuric acid does notreact on copper although it actively reacts on zinc. The etchant for thezinc should also be of such a character that the developedlight-sensitive coating area 24 is passive to it; likewise, thelight-sensitive coa-ting 24 should be passive to the action of the Figs.7-12 show a modification of the process of the previous figures.

Referring to Fig. 7 there is shown, in dotted lines, a cathode matrix ofthe type hereinbefore referred to and which may comprise a metal plateI0 one face of which is provided with a multitude of pits filled flushwith the surface with electrically non-conductive material Il. such asBakelite. the surface therefore comprising a multitude of 'electricallynon-conductive areas delimited by crossed lanes of conductive areas,these lanes corresponding in 'pattern to the pattern of the screen to beproduced. Priorto the electroforming step the screen is covered with astripping layer-e. g., wax, which is ap- Dlied in such a thin coat that,while it does not prevent electrodeposition, it does render the entiresurface of the matrix non-adherent thereto. The matrix being thusprepared, there is electroformedV on it a screen of nickel indicated bythe numeral 42, and thereupon and before the e1ectroformed screen isstripped, its interstices or apertures are filled with a plasticsubstance I3.

such as wax. -Any surplus wax of which, of course, there will always besome is then rubbed off until the crowns 43a of the screen wires areexposed and free from it. The entire surface is then smeared with finelydivided graphite (fiocculent graphite being a desirable form) whichrenders the surfaces of the plastic fillings electrically conductive andcapable of taking an elecvtroplated deposit. The surface is then brushedto remove any graphite that lies on the crowns of the screen wires inorder that they also may be capable of receiving an adherent;electroplated deposit. There is then electroplated on the surface thusprepared a heavy layer 44 of copper.

The structure thus formed is then stripped from the matrix and the waxand graphite washed out with acetone or other solvent accompanied bybrushing .and scrubbing. The stripped structure with the wax removed isthenused as a cathode in a nickel electroplating bath (the surface ofthe copper having been properly masked by the application of a resist inaccordance with well-known methods), the result of 'which is that thewires of the screen and the areas of the copper layer exposed by theremoval of the wax are covered with a layer of nickel Il `which formswebs closing the apertures in the screen. This layer of nickel forreasons that will portions would serve as the screen units Aper linearinch are increased or decreased from the assumed numbers. 4 The nextstep `(see Fig. 9) is to'apply a lightsensitive layer of photo-engraversglue or lightsensitive shellac to the surface of the copper and,`

after the design 45 has been photoprinted there on and developed inaccordance with Well-known methods, the structure of Fig. 9 is subjectedto the action of an etchant which does not affect the glue or the nickelbut does'etch the copper. A suitable etchant is diluted chromic acidinasmuchv as it answers the requirements just referred to. In brief, thephotoprinting process may be similar to that described with respect tothe first described process. If photo-engravers glue is used, it shouldbe hardened by baking in the usual way.

The result of the copper etching process is shown in Fig. 10 wherethepdesign in glue is supported by a ridge 46 of copper. This ridge con-The glue (if glue be used) is then removed by the application of causticpotash and the copper ridges 46 etched out with chromic acid, resultingin the structure `of Fig. 11. After removing the resist that has beenemployed in the previous step. the entire structure is treatedanodically in a dilute sulphuric acid bath which results in etching thethin nickel layer, which procedure is arrested when passages 50 from thedesign area 5l around the wires of the screen and to its rear face havebeen opened up. As in the case of the nickel layer 30 of the firstprocess described, the

. purpose in making the nickel layer 41 as thin as possible as comparedwith the heavy layer 49 is so that the passages referred to may beopened up before any substantial amount of material has been removedfrom the heavy nickel layer. As in the case of the nickel layer 30 rstdescribed herein, the only function that the thin nickel layer 41performs is that of a base upon which the heavy layer 49 of nickel maybe electroplated, and therefore the layer 41 need be no thicker norstronger than is necessary to serve this purpose and to withstandwhatever handling is necessary before the heavy layer has beendeposited.

As in the process rst described (Figs. 1-6), other combinations ofmetals and light-sensitive material may be adopted, provided they lendthemselves to the principles of selective etching that have -beenhereinbefore stated.

I have described above certain methods of practicing the invention,including a preferred f method, but I Wish it to be understood thatthese methods are illustrative. and not limitative of the invention andthat still other methods can be practiced, including varying the orderin which the several steps shall be carried out, and 'such 'variationsstill fall Within the spirit'and scope of my invention as set' forth inthe claims.

I claim:

1.'The process of producing a stencil, which comprises closing theapertures in a nickel screen k with thin Webs of nickel, electroplatingon the,

surface of the webs and the screen lands an unbroken heavy layer ofcopper, applying to the layer of copper a design in baked photographersglue, etching the copper until it is undercut beneath the marginal areasof the design, electroplating a thick layer of nickel on the areasexposed by the etching step thereby adding a continuous metal layer tothe surfaces-delimited by the design areas, removing the glue, etchingaway the copper left unprotected by the removal of the glue, and thenetching the entire structure until ink-feeding passages have been openedfrom the design areas of the heavy layer of nickel through the thinlayer of nickel to the rear face of the screen.

2. The process of producing mesh fabric sten-I cil, whichcomprisessuperimposing on one face of a sheet of nickel screen a solidlayer of copper, blocking out a design on said layer of copper by theapplication of a coating of material passive to electrolytic deposition,.applying to the opposite face ofthe screen a solid thin layer ofnickel, etching the copper layer until the portions not covered by theblocking-out coating are slightly undercut beneath the blocking-outcoating, electroplating a solid layer of nickel on the surface exposedby the etching operation thereby adding a continuous metal layer to thesurfaces delimited by the design areas, removing the blockingoutcoating, etching the portions of the copper layer remaining after thebefore-mentioned applying to the opposite face of the screen a solid lthin layer of metal passive to saifA etchant, etching the superimposedlayer until it has-been slightly undercut beneath the blocking-outcoating, electroplating a solid layer of metal likewise passive to saidetchant on the surface exposed by the'rst-mentioned etching operationthereby adding a continuous metal layer to the surfaces delimited by thedesign areas, removing the blockingout coating, etching the portions ofthe superimposed layer remaining after the said etching operation untilthey havebeen removed, and then removing the layer` on the said oppositeface of the screen.v

A 4. The process of'producing mesh fabric stencil, which comprisessuperimposing on one face of a sheet of nickel screen a solid layer ofanother metal active to an etchant to which the screen is passive,blocking out a design on said superimposed layer by the application of acoating of material passive to electrolytic deposition, applying to theopposite face of the screen a solid thin layer of nickel, etching thesuperimposed layer until it has been slightly undercut beneath theblocking-out coating, the thickness of said superimposed layer being soadjusted that when the undercutting is-completed the great part of thematerial of said layer not protected by the coat willbe removed,electroplating a solid vlayer of metal likewise passive to said etchanton the surface exposed by the first-mentioned etching operation therebyadding a continuous metal layer to the surfaces delimited by the designareas, removing the blocking-out coating, etching the portions'of thesuperimposed layer remain-ing after the said etching operation untilthey have been removed, and then removing the layer on the said oppositeface of the screen.

5. The process of producing mesh fabric stencil, ,which comprisessuperimposing on one face of a sheet of nickel screen a solid layer ofanother metal active to an etchant to which the screen is passive,blocking out a design on said superimposed layer by the application of acoating of material passive to electrolytic'deposition. applying to theopposite face of the screen a solid thin layer of metal passive to saidetchant, etching the superimposed layer until the portions not coveredby the blocking-out coating are at least nearly all removed,electroplating a solid layer of nickel on the surface exposed by thefirstmentioned etching operation thereby adding a continuousl metallayer to the surfaces delimited by the design areas, removing theblockingout coating, etching the portions of the superimposed layerremaining after the said'etching operation until they have been removed,.and the layer on the said'opposite face screen is passive, blocking'out a design on said superimposed layer by the application of a coatingof material passive to electrolytic deposition,

applying to the opposite face of the screen,` a solid thin layer ofmetal passive to said etchant, etching the superimposed layer until ithas been slightly undercut beneath the blocking-out coating, thethickness of the said superimposed layer ybeing so adjusted that whenthe undercutting is '1. 'Ihe process of producing mesh fabric stencil,which comprises superimposing on one face of a sheet of metal screen asolid layer of another metal than that of the screen, blocking out adesign on said layer bythe application of a coat of material passive toelectrolytic deposition, applying to the opposite face of the screen athin second solid layer of metal, etching the iirstmentioned layer untilthe portions not covered by the blocking-out' coat are substantially allre moved, electroplating on the surface exposed by said etching a third'layer of metal thereby adding a continuous metal layer to the surfacesde- 9. The process of producing vmesh fabric stenc il, which comprisessuperimposing on one face of a sheet of metal screen a solid layer ofmetal different from that of the screen, the metal of the superimposedlayer being active to an etchant to which the screen is passive,blocking out a design on the superimposed layer by coating with materiallikewise passive to said etchant and also to electrolytic deposition,applying to the other face of the screen a solid layer of metal alsopassive to said etchant, etching awa-y su-bstantially al1 of thesuperimposed layer over those areas not covered by said coating untilthe said layer has lbeen undercut beneath the said coating,electroplating a layer of metal over the areas exposed by the etchingoperation thereby adding a continuous metal layer to the surfacesdelimited by the design areas, removing the coating and by means of saidetchantfetching the material of the superimposed'layer remaining afterthe first etching operation and underlying the design area from whichthe coating has Ibeen removed, and removing the layer that has beenapplied to the said other face of the screen. r

10. The process of producing a stencil, which comprises closing theapertures in metal screen with thin webs of metal, applying to thesurface `of the webs and the screen lands an unbroken heavy layer ofmetal active to an etchant to which the screen and the webs are passive,blocking out a design on the said heavy layer with limited by the designareas, etching awayiheM-material alscipas'sive to the said etchant,etching portions of the first layer remaining after' the first etchingoperation until the said portions are entirely removed, and thenremoving the second layer, Vthe metals of the several layers, theetchant, and the blocking-out material being so chosen that the etchanthas a selective action on the metal of the second layer to the exclusionof the metal of, the screen of the second layer and the blocking-outmaterial, and the blocking-out material is passive tothe action of anelectrolyte from which the metals of the second layer and the thirdlayer` are deposited.

l 8. The process of producing mesh fabric stencil, which comprisessuperimposingL on one face of a sheet of metal screen a solid layer ofmetal different from that of the screen, one of the metals being activeto an etchant to which. the

v otheris passive, blockingout a design on the superimposed layer bycoating with material like- Awise passive to said etchant and also toelectrolytic deposition, applying to the other face of the screen asolid layer of metal also passive to said said.` heavy layer with saidetchant leavin-g the design in relief, applying to the areas exposed bysaid etching operation a heavy layer of metal passive to saidetohant'thereby adding a continuous metal layer to the surfacesdelimited by the design areas, removing'theblocking-out material,etching away by means of said etchant 40 those portions of thefirst-mentioned heavy layer etching said heavy layer leaving the designinrelief, applying to the areas exposed by the said etching operation aheavy layer of metal, thereby adding a continuous metal layer to thesurfaces etchant, etching away the superimposed hiverl denmited by thedesign areasremcvingtne blockrial of the superimposed layer remainingafter the ilrst etching operation -and underlying the design 'area fromwhich the coating has been removed, and removing the layer that has beenap- 55 plied to the said other face of the screen.

ing layer, etching away those portions of the first-mentioned heavylayer remaining after the first-mentioned etching operation, and thenremoving the said webs until connecting passages are opened leading fromthe design areas to the rear face of the screen, the etching agentemployed in each etching operation being active only to the metal of thefirst-mentioned heavy layer.

EDWARD O. NO RRIS.l

